The Dynamic Ergodic Divertor (DED) for TEXTOR-94

Abstract

A Dynamic Ergodic Divertor (DED) is under construction for TEXTOR‐94. The ergodization will be achieved by a set of 16 in‐vessel perturbation — plus two compensation — coils located at the high field side of TEXTOR‐94. The coils follow helically the magnetic field lines for one toroidal turn of a preselected “resonant” magnetic flux surface and are individually fed outside the vessel allowing a large flexibility for possible interconnections. The DED‐system will operate at DC or several fixed frequencies up to 10 kHz. Different and adapted modelling efforts have been undertaken both for the ergodic area and the laminar zone.The basic techniques for the ergodic zone are field line mapping and field line tracing; the analysis provides the magnetic field structure in form of Poincaré plots and the transport coeffcients for the magnetic field lines. For the laminar zone a modelling is used which takes into account the typical aspects of the scrape‐off layer physics. A low frequency operation of the DED will distribute the heat flux over the relatively large area of the divertor target plate. The calculations show that the high frequency operation should impose a torque on the plasma edge which is of similar size as the one imposed by tangential NBI.

Identification and analysis of transport domains in the stochastic boundary of TEXTOR-DED for different mode spectra

“…At the TEXTOR tokamak the dynamic ergodic divertor (DED) was designed as a flexible setup to investigate the generic features of stochastic magnetic boundaries [10]. As visualized in figure 1 it consists of a set of 16 + 2 coils implemented into the vacuum vessel and winding helically around the torus at the high field side (HFS).…”

Fractal structure of the magnetic field in the laminar zone of the Dynamic Ergodic Divertor of the Torus Experiment for Technology-Oriented Research (TEXTOR-94)

“…[5][6][7][8][9][10][11][12][13][14][15][16][17] have shown that the relative radial extensions of the laminar and the ergodic zones at the plasma edge strongly depend on the plasma parameters ͑plasma ␤ pol , the plasma current I p ), as well as on the divertor current. Particularly, it was found that the increase of the divertor current ͑or decrease of ␤ pol ) does not necessarily lead to a growth of field line diffusivity, which is proportional to the particle diffusion coefficient ͑see Refs.…”

High-speed tangentially viewing soft x-ray camera to study magnetohydrodynamic fluctuations in toroidally confined plasmas (invited)

“…A tokamak has the advantages of a simpler geometry and a more pronounced MHD activity. Furthermore, TEXTOR is presently being equipped with a helical divertor 15 and then we hope to get pronounced structures on demand. …”